In a conference attended by many participants, an audio conference system is used in which voice of a speaker is picked up with a microphone, amplified with an amplifier, and sent out over a speaker in a conference hall to make the voice of the speaker heard by all the participants.
In such an audio conference system, a large number of microphones, corresponding to the number of participants, are used. In a conventional audio conference system, a participant presses an utterance request button provided to a microphone upon making an utterance so that an utterance request command is transmitted from the microphone to a master control. The master control receiving the command performs certain utterance control.
The certain utterance control is: a process of allocating a communication channel to the microphone; and a process of transmitting a communication channel notification together with an utterance permission command to the microphone, both of which are performed by the master control receiving the utterance request command. When a speech is input to the microphone that has received the communication channel notification and the utterance permission command, the speech is output from, for example, a speaker via the master control.
If a communication channel between a microphone and the master control is a radio communication channel, the allocation of a communication channel performed by the master control is allocation control of frequencies to be used.
Among such audio conference systems in which communications between microphones and a master control are controlled through a plurality of radio channels, an audio conference system is known that performs radio channel allocation inhibition control to prevent communication jamming (for example, interference between electric waves) while being used together with another system using radio communication (for example, see Patent Document 1).
With an audio conference system disclosed in Patent Document 1, utterances made by participants in a conference can be mandatory limited by a master control.
FIG. 7 depicts an exemplary configuration of a conventional audio conference system. In FIG. 7, the audio conference system includes: extension microphones 100 including a priority microphone (hereinafter referred to as a “P microphone”) 100a with which the chair of a conference, e.g., a chairman, can mandatory terminate an utterance of other participants when an utterance is being made with a microphone having an utterance permission, and general microphones 100b used by general participants; a master control 200 that receives utterance request commands and speeches transmitted from the extension microphones 100 and, in response thereto, transmits an utterance permission command, performs communication control including allocation control of frequencies to be used, and outputs the speeches transmitted from extension microphones via a speaker; and an antenna 300 that makes the extension microphones 100 and the master control 200 communicate, receives radio signals emitted from the extension microphones 100 and notifies the master control of the reception, and transmits, for example, a signal sent from the master control 200 to the extension microphones 100 as a radio signal.
An utterance control flow in the conventional audio conference device will be described with reference to the sequence diagram in FIG. 8. In FIG. 8, process steps are denoted as S400, S401, and so on.
While an utterance is being made with a general microphone 100b that has received the utterance permission command (S400), a collective utterance termination button, which is not shown in the figure, of the P microphone 100a is pressed and a collective utterance termination command C13 is transmitted to the master control 200 (S401). The master control 200, triggered by the received collective utterance termination command C13, performs a collective utterance termination process and transmits a collective utterance termination command C24 to the general microphone 100b (S402).
The general microphone 100b receiving the collective utterance termination command C24 performs an utterance termination process. A speech signal input thereafter is not transmitted to the master control 200 (S403). When an utterance request button, which is not shown in the figure, of the general microphone 100b is pressed after the utterance process is halted, an utterance request command C31 is transmitted to the master control 200 (S404).
The master control 200 receiving the utterance request command C31 performs an utterance permission process and transmits an utterance permission command C23 to the general microphone 100b (S405). The general microphone 100b receiving the utterance permission command C23 can transmit a speech signal input thereto to the master control 200 (S406).
As described above, the general microphone 100b of which the utterance therewith has been mandatory terminated through the collective utterance termination process (S402) can be used to make an utterance (S405 and S406) by again performing the utterance request process (S404). Therefore, to stop the utterance again, the collective utterance termination button of the P microphone 100a needs to be pressed again (S407) to transmit the collective utterance termination command C13 to the master control 200 so that the collective utterance termination process is performed (S408 and S409).
Unfortunately, if the utterance request is transmitted again (S409 and S41) from the general microphone 100b thereafter, the utterance therewith will be permitted in a similar manner.
As described above, in the conventional audio conference system, even if the chair of a conference collectively terminates the utterance permission of microphones used by other speakers to make the conference proceed smoothly, when the utterance request button of a general microphone 100b is pressed, an utterance can be made therewith. Thus, control of an utterance with the general microphone 100b cannot be maintained.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2005-333498